A large number of generic-type gas turbine components are known from the prior art. A turbine blade, for example, with cooling air openings which open onto the surface of the turbine blade around which hot gas flows, as film-cooling holes, for example, may be understood by the gas turbine component which is referred to in the introduction. Also, a rotor disk for a gas turbine, in which mostly radially extending bores are arranged for the passage of air, is to be understood by a gas turbine component within the meaning of the present patent application. Also, turbine stator blade carriers, which are known from the prior art, have passages for the passage of cooling air, used later for cooling, which open onto its surface.
Common to all the said gas turbine components is that the material which directly surrounds the passage is subjected to specific loads. In the case of turbine stator blades and rotor blades, particularly thermal and mechanical loads occur. Rotor disks are also particularly mechanically loaded on account of the centrifugal forces which occur. Cyclic loads can also occur. The loads lead to stresses which on account of the presence of the passages—which in most cases are created by bores—are further increased close to the surface in the immediate surroundings of the passage (stress concentrations). Regardless of the origin of the load, the increases may be impermissibly large, which limits the service life of the corresponding components.
Therefore, cracks can develop in the components referred to in the introduction, starting from the mouth region of the passages, which cracks have to be monitored and lead to exchange of the components when a critical crack length is exceeded.
It can also be that calculations carried out during the construction of the components show that, on account of an incipient crack-stress cycle number which is excessively low, the desired calculated service life is not achieved.
Thus known, for example, are turbine blades which with the aid of passages which extend obliquely through their component wall direct cooling air to their outer side, forming a protective film there. In order to achieve a particularly good protective effect, an expansion recess for the cooling air is provided at the hot gas-side passage end according to GB 2 438 861 A, for example. A similar measure for improving the cooling effect is known from U.S. Pat. No. 5,653,110 A1, according to which the passage end opens onto a surface which is corrugated on the hot gas side. Also, in the case of the known developments, there is the above-described risk that cracks can develop due to thermomechanical stresses in the mouth region.